The present invention relates to an anti-vibration apparatus and an exposure apparatus. More particularly, the present invention is suitably applied to an active type anti-vibration apparatus wherein an anti-vibration bed is driven by an actuator so that vibrations of the anti-vibration bed are suppressed. The present invention is also suitably applied to an exposure apparatus having the anti-vibration apparatus.
With the achievement of high accuracies of precision apparatus, such as step-and-repeat reduction projection type exposure apparatuses, i.e. steppers, there has occurred a need of controlling, on the micro-G level, microvibrations acting on a base plate (anti-vibration bed) from a floor where a stepper, or the like, is installed.
Various vibration-isolating pads are used to support an anti-vibration bed: For example, mechanical dampers having a compression coil spring placed in a damping fluid, and pneumatic dampers. The vibration-isolating pads per se, have a certain degree of centering function.
In particular, pneumatic spring type anti-vibration apparatuses having pneumatic dampers enable the spring constant to be set at a small value and are capable of suppressing vibrations of about 10 Hz or more. Therefore, this type of anti-vibration apparatus has widely been employed to support precision apparatus.
Recently, active type anti-vibration apparatuses have been proposed to move beyond the limitations of conventional passive type anti-vibration apparatuses. In the active type, vibrations of an anti-vibration bed are detected with a sensor, and an actuator is driven on the basis of the output of the sensor, thereby effecting vibration control. Thus, it is possible to provide an ideal vibration-isolating effect having no resonance peak in a low-frequency control band.
In an exposure apparatus, e.g. a stepper, an XY-stage (wafer stage), which is accelerated and decelerated to a considerable extent, is mounted on a base plate held by vibration-isolating pads. Therefore, the center of gravity of the exposure apparatus main body shifts at the same time as the XY-stage moves. When the center of gravity of the exposure apparatus main body has shifted in accordance with the stage movement, an active type anti-vibration apparatus provided in the exposure apparatus effects positioning of the XY-stage with respect to the initial position by a position control loop. As the amount of movement of the stage increases, the amount of change of the gravity center of the exposure apparatus main body also increases. Consequently, the base plate, on which the exposure apparatus main body is mounted, also inclines to a considerable extent. As the amount of change of the gravity center of the exposure apparatus main body increases, the amount of inclination of the base plate also increases, and the thrust required for the actuator to correct the inclination also increases.
In such an anti-vibration apparatus, a large amount of heat is generated from the actuator, and there is a large change in the temperature of an environment where the exposure apparatus is placed. The environmental temperature change affects the measuring accuracy of a laser interferometer that measures the position of the XY-stage, giving rise to a problem, such as degradation of the stage positioning accuracy.
To solve such a problem, it is conceivable to increase the gain of the position control loop of the anti-vibration apparatus. By doing so, the position control responsivity is improved, but the vibration-isolating performance is degraded because vibrations of the floor are transmitted to the exposure apparatus main body. Therefore, it is not an effective method. Accordingly, it is urgent to develop an apparatus capable of suppressing an environmental temperature change while ensuring the position control responsivity to a certain extent without degrading the vibration-isolating performance.